Messaging in a parallel computer using remote direct memory access (‘RDMA’)

ABSTRACT

Messaging in a parallel computer using remote direct memory access (‘RDMA’), including: receiving a send work request; responsive to the send work request: translating a local virtual address on the first node from which data is to be transferred to a physical address on the first node from which data is to be transferred from; creating a local RDMA object that includes a counter set to the size of a messaging acknowledgment field; sending, from a messaging unit in the first node to a messaging unit in a second node, a message that includes a RDMA read operation request, the physical address of the local RDMA object, and the physical address on the first node from which data is to be transferred from; and receiving, by the first node responsive to the second node&#39;s execution of the RDMA read operation request, acknowledgment data in the local RDMA object.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of and claims priorityfrom U.S. patent application Ser. No. 13/167,911, filed on Jun. 24,2011.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention is data processing, or, more specifically,methods, apparatus, and products for messaging in a parallel computerusing remote direct memory access (‘RDMA’).

2. Description of Related Art

The development of the EDVAC computer system of 1948 is often cited asthe beginning of the computer era. Since that time, computer systemshave evolved into extremely complicated devices. Today's computers aremuch more sophisticated than early systems such as the EDVAC. Computersystems typically include a combination of hardware and softwarecomponents, application programs, operating systems, processors, buses,memory, input/output devices, and so on. As advances in semiconductorprocessing and computer architecture push the performance of thecomputer higher and higher, more sophisticated computer software hasevolved to take advantage of the higher performance of the hardware,resulting in computer systems today that are much more powerful thanjust a few years ago.

In high-performance computing (HPC), high-speed communications adaptersuse remote data memory access (RDMA) operations to move data between thememory of a local computer and the memory of a remote computer. Thehigh-speed adapters which perform these operations characteristicallywork under a software stack known as Open Fabrics EnterpriseDistribution (OFED).

SUMMARY OF THE INVENTION

Messaging in a parallel computer using remote direct memory access(‘RDMA’), the parallel computer including a plurality of nodes, eachnode including a messaging unit, including: receiving, by a kernel ofthe first node through an application programming interface (‘API’), asend work request, the send work request including: a local virtualaddress on the first node from which data is to be transferred; and aspecification of a size of data to be transferred from the first node toa second node, wherein the size of data to be transferred from the firstnode to a second node is larger than a messaging packet size for sendingdata from the first node to a second node; responsive to the send workrequest: translating, by the kernel of the first node, the local virtualaddress on the first node from which data is to be transferred to aphysical address on the first node from which data is to be transferredfrom; creating, by the kernel of the first node, a local RDMA objectthat includes a counter set to the size of a messaging acknowledgmentfield; sending, from a messaging unit in the first node to a messagingunit in a second node, a message that includes a RDMA read operationrequest, the physical address of the local RDMA object, and the physicaladdress on the first node from which data is to be transferred from; andreceiving, by the first node responsive to the second node's executionof the RDMA read operation request, acknowledgment data in the localRDMA object.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescriptions of exemplary embodiments of the invention as illustrated inthe accompanying drawings wherein like reference numbers generallyrepresent like parts of exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 sets forth example apparatus for messaging using RDMA accordingto embodiments of the present invention.

FIG. 2 sets forth a block diagram of an example compute node useful in aparallel computer capable of messaging using RDMA according toembodiments of the present invention.

FIG. 3A sets forth a block diagram of an example Point-To-Point Adapteruseful in systems for messaging using RDMA in a parallel computeraccording to embodiments of the present invention.

FIG. 3B sets forth a block diagram of an example Global CombiningNetwork Adapter useful in systems for messaging using RDMA in a parallelcomputer according to embodiments of the present invention.

FIG. 4 sets forth a line drawing illustrating an example datacommunications network optimized for point-to-point operations useful insystems capable of messaging using RDMA in a parallel computer accordingto embodiments of the present invention.

FIG. 5 sets forth a line drawing illustrating an example globalcombining network useful in systems capable of messaging using RDMA in aparallel computer according to embodiments of the present invention.

FIG. 6 sets forth a flow chart illustrating an example method formessaging in a parallel computer using RDMA according to embodiments ofthe present invention.

FIG. 7 sets forth a flow chart illustrating an example method formessaging in a parallel computer using RDMA according to embodiments ofthe present invention.

FIG. 8 sets forth a flow chart illustrating an example method formessaging in a parallel computer using RDMA according to embodiments ofthe present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary methods, apparatus, and products for messaging in a parallelcomputer using RDMA in accordance with the present invention aredescribed with reference to the accompanying drawings, beginning withFIG. 1. FIG. 1 sets forth example apparatus for messaging in a parallelcomputer using RDMA according to embodiments of the present invention.The apparatus of FIG. 1 includes a parallel computer (100), non-volatilememory for the computer in the form of a data storage device (118), anoutput device for the computer in the form of a printer (120), and aninput/output device for the computer in the form of a computer terminal(122). The parallel computer (100) in the example of FIG. 1 includes aplurality of compute nodes (102). The compute nodes (102) are coupledfor data communications by several independent data communicationsnetworks including a high speed Ethernet network (174), a Joint TestAction Group (‘JTAG’) network (104), a global combining network (106)which is optimized for collective operations using a binary tree networktopology, and a point-to-point network (108), which is optimized forpoint-to-point operations using a torus network topology. The globalcombining network (106) is a data communications network that includesdata communications links connected to the compute nodes (102) so as toorganize the compute nodes (102) as a binary tree. Each datacommunications network is implemented with data communications linksamong the compute nodes (102). The data communications links providedata communications for parallel operations among the compute nodes(102) of the parallel computer (100).

The compute nodes (102) of the parallel computer (100) are organizedinto at least one operational group (132) of compute nodes forcollective parallel operations on the parallel computer (100). Eachoperational group (132) of compute nodes is the set of compute nodesupon which a collective parallel operation executes. Each compute nodein the operational group (132) is assigned a unique rank that identifiesthe particular compute node in the operational group (132). Collectiveoperations are implemented with data communications among the computenodes of an operational group. Collective operations are those functionsthat involve all the compute nodes of an operational group (132). Acollective operation is an operation, a message-passing computer programinstruction that is executed simultaneously, that is, at approximatelythe same time, by all the compute nodes in an operational group (132) ofcompute nodes. Such an operational group (132) may include all thecompute nodes (102) in a parallel computer (100) or a subset all thecompute nodes (102). Collective operations are often built aroundpoint-to-point operations. A collective operation requires that allprocesses on all compute nodes within an operational group (132) callthe same collective operation with matching arguments. A ‘broadcast’ isan example of a collective operation for moving data among compute nodesof an operational group. A ‘reduce’ operation is an example of acollective operation that executes arithmetic or logical functions ondata distributed among the compute nodes of an operational group (132).An operational group (132) may be implemented as, for example, an MPI‘communicator.’

‘MPI’ refers to ‘Message Passing Interface,’ a prior art parallelcommunications library, a module of computer program instructions fordata communications on parallel computers. Examples of prior-artparallel communications libraries that may be improved for RDMA in aparallel computer according to embodiments of the present inventioninclude MPI and the ‘Parallel Virtual Machine’ (‘PVM’) library. PVM wasdeveloped by the University of Tennessee, The Oak Ridge NationalLaboratory and Emory University. MPI is promulgated by the MPI Forum, anopen group with representatives from many organizations that define andmaintain the MPI standard. MPI at the time of this writing is a de factostandard for communication among compute nodes running a parallelprogram on a distributed memory parallel computer. This specificationsometimes uses MPI terminology for ease of explanation, although the useof MPI as such is not a requirement or limitation of the presentinvention.

Some collective operations have a single originating or receivingprocess running on a particular compute node in an operational group(132). For example, in a ‘broadcast’ collective operation, the processon the compute node that distributes the data to all the other computenodes is an originating process. In a ‘gather’ operation, for example,the process on the compute node that received all the data from theother compute nodes is a receiving process. The compute node on whichsuch an originating or receiving process runs is referred to as alogical root.

Most collective operations are variations or combinations of four basicoperations: broadcast, gather, scatter, and reduce. The interfaces forthese collective operations are defined in the MPI standards promulgatedby the MPI Forum. Algorithms for executing collective operations,however, are not defined in the MPI standards. In a broadcast operation,all processes specify the same root process, whose buffer contents willbe sent. Processes other than the root specify receive buffers. Afterthe operation, all buffers contain the message from the root process.

A scatter operation, like the broadcast operation, is also a one-to-manycollective operation. In a scatter operation, the logical root dividesdata on the root into segments and distributes a different segment toeach compute node in the operational group (132). In scatter operation,all processes typically specify the same receive count. The sendarguments are only significant to the root process, whose bufferactually contains sendcount*N elements of a given datatype, where N isthe number of processes in the given group of compute nodes. The sendbuffer is divided and dispersed to all processes (including the processon the logical root). Each compute node is assigned a sequentialidentifier termed a ‘rank.’ After the operation, the root has sentsendcount data elements to each process in increasing rank order. Rank 0receives the first sendcount data elements from the send buffer. Rank 1receives the second sendcount data elements from the send buffer, and soon.

A gather operation is a many-to-one collective operation that is acomplete reverse of the description of the scatter operation. That is, agather is a many-to-one collective operation in which elements of adatatype are gathered from the ranked compute nodes into a receivebuffer in a root node.

A reduction operation is also a many-to-one collective operation thatincludes an arithmetic or logical function performed on two dataelements. All processes specify the same ‘count’ and the same arithmeticor logical function. After the reduction, all processes have sent countdata elements from compute node send buffers to the root process. In areduction operation, data elements from corresponding send bufferlocations are combined pair-wise by arithmetic or logical operations toyield a single corresponding element in the root process' receivebuffer. Application specific reduction operations can be defined atruntime. Parallel communications libraries may support predefinedoperations. MPI, for example, provides the following pre-definedreduction operations:

MPI_MAX maximum MPI_MIN minimum MPI_SUM sum MPI_PROD product MPI_LANDlogical and MPI_BAND bitwise and MPI_LOR logical or MPI_BOR bitwise orMPI_LXOR logical exclusive or MPI_BXOR bitwise exclusive or

In addition to compute nodes, the parallel computer (100) includesinput/output (‘I/O’) nodes (110, 114) coupled to compute nodes (102)through the global combining network (106). The compute nodes (102) inthe parallel computer (100) may be partitioned into processing sets suchthat each compute node in a processing set is connected for datacommunications to the same I/O node. Each processing set, therefore, iscomposed of one I/O node and a subset of compute nodes (102). The ratiobetween the number of compute nodes to the number of I/O nodes in theentire system typically depends on the hardware configuration for theparallel computer (102). For example, in some configurations, eachprocessing set may be composed of eight compute nodes and one I/O node.In some other configurations, each processing set may be composed ofsixty-four compute nodes and one I/O node. Such example are forexplanation only, however, and not for limitation. Each I/O nodeprovides I/O services between compute nodes (102) of its processing setand a set of I/O devices. In the example of FIG. 1, the I/O nodes (110,114) are connected for data communications I/O devices (118, 120, 122)through local area network (‘LAN’) (130) implemented using high-speedEthernet.

The parallel computer (100) of FIG. 1 also includes a service node (116)coupled to the compute nodes through one of the networks (104). Servicenode (116) provides services common to pluralities of compute nodes,administering the configuration of compute nodes, loading programs intothe compute nodes, starting program execution on the compute nodes,retrieving results of program operations on the compute nodes, and soon. Service node (116) runs a service application (124) and communicateswith users (128) through a service application interface (126) that runson computer terminal (122).

The parallel computer (100) of FIG. 1 includes many nodes. In theexample of FIG. 1, two nodes are illustrated in more detail, a firstnode (102 a) and a second (102 b). Each node (102 a, 102 b) includes amessaging unit (101 a, 101 b) for exchanging messages with other nodes,a kernel (103 a, 103 b) to provide operating system type services to thenodes (102 a, 102 b), and computer memory (105 a, 105 b). In the exampleof FIG. 1, the computer memory (105 a, 105 b) includes a local RDMAobject (107 a, 107 b), which is a data structure useful in messaging inthe parallel computer (100) using RDMA according to embodiments of thepresent invention. The computer memory (105 a, 105 b) also includes anAPI (109 a, 109 b), a module of computer program instructions,operations, and classes for initiating a send work request (111).

The parallel computer (100) of FIG. 1 operates generally for messagingin the parallel computer (100) using RDMA. The parallel computer (100)of FIG. 1 includes a plurality of nodes, such as the first node (102 a)and the second node (102 b), that may be embodied as a compute node, anI/O node, or other module of automated computing machinery that forms aparallel computer (100). In the example of FIG. 1, each node (102 a, 102b) includes a messaging unit (101 a, 101 b). The messaging units (101 a,101 b) of FIG. 1 may be embodied, for example, as a communicationsadapter for point-to-point data communications with other nodes in theparallel computer (100), as a library of data communications operationsfor carrying out data communications with other nodes in the parallelcomputer (100), or any combination thereof. In the example of FIG. 1,the messaging units (101 a, 101 b) may carry out data communicationswith other nodes in the parallel computer (100), for example, over atorus network as described with reference to FIGS. 1-4.

The parallel computer (100) of FIG. 1 carries out messaging using RDMAby receiving, by a kernel of the first node through an applicationprogramming interface (‘API’), a send work request (111). The API (109a) of FIG. 1 may include one or more software routines that anapplication-level program can invoke to initiate a send work request(111). In the example of FIG. 1, a work request represents a request forthe recipient of the work request to perform some task. The send workrequest (111) of FIG. 1 is a particular type of work request. The sendwork request (111) of FIG. 1 represents a request for the recipient ofthe send work request (111) to perform the task of sending data toanother node. In the example of FIG. 1, the send work request (111) isreceived by the first node (102 a), and as such, the send work request(111) represents a request for the first node (102 a) to perform thetask of sending data to another node, designated here as the second node(102 b).

In the example of FIG. 1, the send work request includes a local virtualaddress on the first node from which data is to be transferred. Thelocal virtual address points to a location in virtual memory of thefirst node (102 a) that is mapped to actual physical memory of the firstnode (102 a), for example, by a page table that is accessible by thekernel (103 a). In the example method of FIG. 1, the send work request(111) also includes a specification of a size of data that is to betransferred from the first node (102 a) to the second node (102 b).

In the example method of FIG. 1, data can be transferred from the firstnode (102 a) to the second node (102 b) by exchanging messages between amessaging unit (101 a) of the first node (102 a) and a messaging unit(101 b) of the second node (102 b). Such messages may have a predefinedpacket size to include control information such as the address of therecipient, as well as a payload representing the actual data that is tobe transferred. In the example of FIG. 1, the size of data to betransferred from the first node (102 a) to the second node (102 b) islarger than a messaging packet size for sending data from the first node(102 a) to a second node (102 b). Because the size of the data to betransferred from the first node (102 a) to the second node (102 b) islarger than the messaging packet size, transferring the data referencedin the send work request (111) by exchanging messages between themessaging unit (101 a) of the first node (102 a) and the messaging unit(101 b) of the second node (102 b) would necessitate exchanging multiplemessages.

The parallel computer (100) of FIG. 1 further carries out messagingusing RDMA by translating, by the kernel of the first node, the localvirtual address on the first node from which data is to be transferredto a physical address on the first node from which data is to betransferred from. The physical address represents the physical addressin memory from which data is to be transferred. In the example of FIG.1, translating the local virtual address on the first node (102 a) to aphysical address on the first node (102 a) may be carried out, forexample, by looking up the virtual address in a page table stored on thefirst node (102 a), by looking up the virtual address in a translationlookaside buffer (‘TLB’) stored on the first node, by using an addresstranslation algorithm, and so on.

The parallel computer (100) of FIG. 1 further carries out messagingusing RDMA by creating, by the kernel of the first node, a local RDMAobject that includes a counter set to the size of a messagingacknowledgment field. In the example of FIG. 1, a messagingacknowledgment field represents a data structure used to storeacknowledgement data that is sent in response to the receipt of amessage. For example, if the first node (102 a) sent a message to thesecond node (102 b) using the messaging unit (101 a) in the first node(102 a), the first node (102 a) would expect to receive acknowledgmentdata from the second node (102 b) indicating that the message wasreceived by the second node (102 b). Such acknowledgment data mayinclude information used to verify that the message was receivedcorrectly such as, for example, a checksum. In the example of FIG. 1,the acknowledgment data would be written into a messaging acknowledgmentfield in computer memory of the first node (102 a). Because the localRDMA object (107 a) includes a counter set to the size of a messagingacknowledgment field, as acknowledgment data is received by the firstnode (102 a), the first node (102 a) may decrement the counter for thepurpose of determining when all acknowledgment data has been received.In the example of FIG. 1, the size of a messaging acknowledgment fieldmay be expressed in any unit of measure, for example, such as byte,kilobyte, megabyte, and so on.

The parallel computer (100) of FIG. 1 further carries out messagingusing RDMA by sending, from a messaging unit in the first node to amessaging unit in a second node, a message. In the example of FIG. 1,the message includes a RDMA read operation request, the physical addressof the local RDMA object (107 a), and the physical address on the firstnode (102 a) from which data is to be transferred from.

In the example of FIG. 1, a RDMA read operation request is sent from thefirst node (102 a) to the second node (102 b), to prompt the second node(102 b) to read data stored in memory of the first node (102 a) intomemory on the second node (102 b). In such an example, the RDMA readoperation request is accompanied by the physical address on the firstnode (102 a) from which data is to be transferred from, so that thesecond node (102 b) is informed of the address in memory on the firstnode (102 a) that the data is to be read from.

The parallel computer (100) of FIG. 1 further carries out messagingusing RDMA by receiving, by the first node responsive to the secondnode's execution of the RDMA read operation request, acknowledgment datain the local RDMA object. In the example of FIG. 1, acknowledgment datais sent from the recipient of a message to the sender of a message inresponse to the receipt of a message. For example, if the first node(102 a) sent a message to the second node (102 b) using the messagingunit (101 a) in the first node (102 a), the first node (102 a) wouldexpect to receive acknowledgment data from the second node (102 b)indicating that the message was received by the second node (102 b).Such acknowledgment data may include information used to verify that themessage was received correctly such as, for example, a checksum. In theexample of FIG. 1, the acknowledgment data is written into a messagingacknowledgment field in the local RDMA object (107 a) of the first node(102 a).

The arrangement of nodes, networks, and I/O devices making up theexample apparatus illustrated in FIG. 1 are for explanation only, notfor limitation of the present invention. Apparatus capable of messagingusing RDMA according to embodiments of the present invention may includeadditional nodes, networks, devices, and architectures, not shown inFIG. 1, as will occur to those of skill in the art. The parallelcomputer (100) in the example of FIG. 1 includes sixteen compute nodes(102); parallel computers capable of RDMA in a parallel computeraccording to embodiments of the present invention sometimes includethousands of compute nodes. In addition to Ethernet (174) and JTAG(104), networks in such data processing systems may support many datacommunications protocols including for example TCP (Transmission ControlProtocol), IP (Internet Protocol), and others as will occur to those ofskill in the art. Various embodiments of the present invention may beimplemented on a variety of hardware platforms in addition to thoseillustrated in FIG. 1.

Messaging in a parallel computer using RDMA according to embodiments ofthe present invention is generally implemented on a parallel computerthat includes a plurality of compute nodes organized for collectiveoperations through at least one data communications network. In fact,such computers may include thousands of such compute nodes. Each computenode is in turn itself a kind of computer composed of one or morecomputer processing cores, its own computer memory, and its owninput/output adapters. For further explanation, therefore, FIG. 2 setsforth a block diagram of an example compute node (102) useful in aparallel computer capable of messaging using RDMA according toembodiments of the present invention. The compute node (102) of FIG. 2includes a plurality of processing cores (165) as well as RAM (156). Theprocessing cores (165) of FIG. 2 may be configured on one or moreintegrated circuit dies. Processing cores (165) are connected to RAM(156) through a high-speed memory bus (155) and through a bus adapter(194) and an extension bus (168) to other components of the computenode. Stored in RAM (156) is an application program (159), a module ofcomputer program instructions that carries out parallel, user-level dataprocessing using parallel algorithms.

Also stored RAM (156) is a parallel communications library (161), alibrary of computer program instructions that carry out parallelcommunications among compute nodes, including point-to-point operationsas well as collective operations. A library of parallel communicationsroutines may be developed from scratch for use in systems according toembodiments of the present invention, using a traditional programminglanguage such as the C programming language, and using traditionalprogramming methods to write parallel communications routines that sendand receive data among nodes on two independent data communicationsnetworks. Alternatively, existing prior art libraries may be improved tooperate according to embodiments of the present invention. Examples ofprior-art parallel communications libraries include the ‘Message PassingInterface’ (‘MPI’) library and the ‘Parallel Virtual Machine’ (‘PVM’)library.

Also stored in RAM (156) is an operating system (162), a module ofcomputer program instructions and routines for an application program'saccess to other resources of the compute node. It is typical for anapplication program and parallel communications library in a computenode of a parallel computer to run a single thread of execution with nouser login and no security issues because the thread is entitled tocomplete access to all resources of the node. The quantity andcomplexity of tasks to be performed by an operating system on a computenode in a parallel computer therefore are smaller and less complex thanthose of an operating system on a serial computer with many threadsrunning simultaneously. In addition, there is no video I/O on thecompute node (102) of FIG. 2, another factor that decreases the demandson the operating system. The operating system (162) may therefore bequite lightweight by comparison with operating systems of generalpurpose computers, a pared down version as it were, or an operatingsystem developed specifically for operations on a particular parallelcomputer. Operating systems that may usefully be improved, simplified,for use in a compute node include UNIX™, Linux™, Windows XP™, AIX™,IBM's i5/OS™, and others as will occur to those of skill in the art.

The example compute node (102) of FIG. 2 includes several communicationsadapters (172, 176, 180, 188) for implementing data communications withother nodes of a parallel computer. Such data communications may becarried out serially through RS-232 connections, through external busessuch as USB, through data communications networks such as IP networks,and in other ways as will occur to those of skill in the art.Communications adapters implement the hardware level of datacommunications through which one computer sends data communications toanother computer, directly or through a network. Examples ofcommunications adapters useful in apparatus for messaging using RDMAinclude modems for wired communications, Ethernet (IEEE 802.3) adaptersfor wired network communications, and 802.11b adapters for wirelessnetwork communications.

The data communications adapters in the example of FIG. 2 include aGigabit Ethernet adapter (172) that couples example compute node (102)for data communications to a Gigabit Ethernet (174). Gigabit Ethernet isa network transmission standard, defined in the IEEE 802.3 standard,that provides a data rate of 1 billion bits per second (one gigabit).Gigabit Ethernet is a variant of Ethernet that operates over multimodefiber optic cable, single mode fiber optic cable, or unshielded twistedpair.

The data communications adapters in the example of FIG. 2 include a JTAGSlave circuit (176) that couples example compute node (102) for datacommunications to a JTAG Master circuit (178). JTAG is the usual nameused for the IEEE 1149.1 standard entitled Standard Test Access Port andBoundary-Scan Architecture for test access ports used for testingprinted circuit boards using boundary scan. JTAG is so widely adaptedthat, at this time, boundary scan is more or less synonymous with JTAG.JTAG is used not only for printed circuit boards, but also forconducting boundary scans of integrated circuits, and is also useful asa mechanism for debugging embedded systems, providing a convenient “backdoor” into the system. The example compute node of FIG. 2 may be allthree of these: It typically includes one or more integrated circuitsinstalled on a printed circuit board and may be implemented as anembedded system having its own processing core, its own memory, and itsown I/O capability. JTAG boundary scans through JTAG Slave (176) mayefficiently configure processing core registers and memory in computenode (102) for use in dynamically reassigning a connected node to ablock of compute nodes useful in systems for messaging using RDMAaccording to embodiments of the present invention.

The data communications adapters in the example of FIG. 2 include aPoint-To-Point Network Adapter (180) that couples example compute node(102) for data communications to a network (108) that is optimal forpoint-to-point message passing operations such as, for example, anetwork configured as a three-dimensional torus or mesh. ThePoint-To-Point Adapter (180) provides data communications in sixdirections on three communications axes, x, y, and z, through sixbidirectional links: +x (181), −x (182), +y (183), −y (184), +z (185),and −z (186).

The data communications adapters in the example of FIG. 2 include aGlobal Combining Network Adapter (188) that couples example compute node(102) for data communications to a global combining network (106) thatis optimal for collective message passing operations such as, forexample, a network configured as a binary tree. The Global CombiningNetwork Adapter (188) provides data communications through threebidirectional links for each global combining network (106) that theGlobal Combining Network Adapter (188) supports. In the example of FIG.2, the Global Combining Network Adapter (188) provides datacommunications through three bidirectional links for global combiningnetwork (106): two to children nodes (190) and one to a parent node(192).

The example compute node (102) includes multiple arithmetic logic units(‘ALUs’). Each processing core (165) includes an ALU (166), and aseparate ALU (170) is dedicated to the exclusive use of the GlobalCombining Network Adapter (188) for use in performing the arithmetic andlogical functions of reduction operations, including an allreduceoperation. Computer program instructions of a reduction routine in aparallel communications library (161) may latch an instruction for anarithmetic or logical function into an instruction register (169). Whenthe arithmetic or logical function of a reduction operation is a ‘sum’or a ‘logical OR,’ for example, the collective operations adapter (188)may execute the arithmetic or logical operation by use of the ALU (166)in the processing core (165) or, typically much faster, by use of thededicated ALU (170) using data provided by the nodes (190, 192) on theglobal combining network (106) and data provided by processing cores(165) on the compute node (102).

Often when performing arithmetic operations in the global combiningnetwork adapter (188), however, the global combining network adapter(188) only serves to combine data received from the children nodes (190)and pass the result up the network (106) to the parent node (192).Similarly, the global combining network adapter (188) may only serve totransmit data received from the parent node (192) and pass the data downthe network (106) to the children nodes (190). That is, none of theprocessing cores (165) on the compute node (102) contribute data thatalters the output of ALU (170), which is then passed up or down theglobal combining network (106). Because the ALU (170) typically does notoutput any data onto the network (106) until the ALU (170) receivesinput from one of the processing cores (165), a processing core (165)may inject the identity element into the dedicated ALU (170) for theparticular arithmetic operation being perform in the ALU (170) in orderto prevent alteration of the output of the ALU (170). Injecting theidentity element into the ALU, however, often consumes numerousprocessing cycles. To further enhance performance in such cases, theexample compute node (102) includes dedicated hardware (171) forinjecting identity elements into the ALU (170) to reduce the amount ofprocessing core resources required to prevent alteration of the ALUoutput. The dedicated hardware (171) injects an identity element thatcorresponds to the particular arithmetic operation performed by the ALU.For example, when the global combining network adapter (188) performs abitwise OR on the data received from the children nodes (190), dedicatedhardware (171) may inject zeros into the ALU (170) to improveperformance throughout the global combining network (106).

In the example of FIG. 2, the compute node (102) may utilize messageunit (‘MU’) hardware for I/O data transport across I/O links and, forflexible I/O configurations, across an I/O torus. An I/O softwarearchitecture may specify a network layer on which I/O services arebuilt. The network layer components may be modeled after the OpenFabrics RDMA framework or OpenFabrics Enterprise Distribution (‘OFED’)framework, an organization of companies and individuals providing opensource software in the high-performance-computing (‘HPC’) arena. Assuch, internal network interfaces may be modeled after the OFEDinterfaces and processes running in the I/O node environment maycommunicate over I/O links using standard OFED RDMA verbs.

For further explanation, FIG. 3A sets forth a block diagram of anexample Point-To-Point Adapter (180) useful in systems for messagingusing RDMA according to embodiments of the present invention. ThePoint-To-Point Adapter (180) is designed for use in a datacommunications network optimized for point-to-point operations, anetwork that organizes compute nodes in a three-dimensional torus ormesh. The Point-To-Point Adapter (180) in the example of FIG. 3Aprovides data communication along an x-axis through four unidirectionaldata communications links, to and from the next node in the −x direction(182) and to and from the next node in the +x direction (181). ThePoint-To-Point Adapter (180) of FIG. 3A also provides data communicationalong a y-axis through four unidirectional data communications links, toand from the next node in the −y direction (184) and to and from thenext node in the +y direction (183). The Point-To-Point Adapter (180) ofFIG. 3A also provides data communication along a z-axis through fourunidirectional data communications links, to and from the next node inthe −z direction (186) and to and from the next node in the +z direction(185).

For further explanation, FIG. 3B sets forth a block diagram of anexample Global Combining Network Adapter (188) useful in systems formessaging using RDMA according to embodiments of the present invention.The Global Combining Network Adapter (188) is designed for use in anetwork optimized for collective operations, a network that organizescompute nodes of a parallel computer in a binary tree. The GlobalCombining Network Adapter (188) in the example of FIG. 3B provides datacommunication to and from children nodes of a global combining networkthrough four unidirectional data communications links (190), and alsoprovides data communication to and from a parent node of the globalcombining network through two unidirectional data communications links(192).

For further explanation, FIG. 4 sets forth a line drawing illustratingan example data communications network (108) optimized forpoint-to-point operations useful in systems capable of messaging usingRDMA according to embodiments of the present invention. In the exampleof FIG. 4, dots represent compute nodes (102) of a parallel computer,and the dotted lines between the dots represent data communicationslinks (103) between compute nodes. The data communications links areimplemented with point-to-point data communications adapters similar tothe one illustrated for example in FIG. 3A, with data communicationslinks on three axis, x, y, and z, and to and fro in six directions +x(181), −x (182), +y (183), −y (184), +z (185), and −z (186). The linksand compute nodes are organized by this data communications networkoptimized for point-to-point operations into a three dimensional mesh(105). The mesh (105) has wrap-around links on each axis that connectthe outermost compute nodes in the mesh (105) on opposite sides of themesh (105). These wrap-around links form a torus (107). Each computenode in the torus has a location in the torus that is uniquely specifiedby a set of x, y, z coordinates. Readers will note that the wrap-aroundlinks in the y and z directions have been omitted for clarity, but areconfigured in a similar manner to the wrap-around link illustrated inthe x direction. For clarity of explanation, the data communicationsnetwork of FIG. 4 is illustrated with only 27 compute nodes, but readerswill recognize that a data communications network optimized forpoint-to-point operations for use in messaging in a parallel computerusing RDMA in accordance with embodiments of the present invention maycontain only a few compute nodes or may contain thousands of computenodes. For ease of explanation, the data communications network of FIG.4 is illustrated with only three dimensions, but readers will recognizethat a data communications network optimized for point-to-pointoperations for use in messaging in a parallel computer using RDMA inaccordance with embodiments of the present invention may in facet beimplemented in two dimensions, four dimensions, five dimensions, and soon. Several supercomputers now use five dimensional mesh or torusnetworks, including, for example, IBM's Blue Gene Q™.

For further explanation, FIG. 5 sets forth a line drawing illustratingan example global combining network (106) useful in systems capable ofmessaging using RDMA according to embodiments of the present invention.The example data communications network of FIG. 5 includes datacommunications links (103) connected to the compute nodes so as toorganize the compute nodes as a tree. In the example of FIG. 5, dotsrepresent compute nodes (102) of a parallel computer, and the dottedlines (103) between the dots represent data communications links betweencompute nodes. The data communications links are implemented with globalcombining network adapters similar to the one illustrated for example inFIG. 3B, with each node typically providing data communications to andfrom two children nodes and data communications to and from a parentnode, with some exceptions. Nodes in the global combining network (106)may be characterized as a physical root node (202), branch nodes (204),and leaf nodes (206). The physical root (202) has two children but noparent and is so called because the physical root node (202) is the nodephysically configured at the top of the binary tree. The leaf nodes(206) each has a parent, but leaf nodes have no children. The branchnodes (204) each has both a parent and two children. The links andcompute nodes are thereby organized by this data communications networkoptimized for collective operations into a binary tree (106). Forclarity of explanation, the data communications network of FIG. 5 isillustrated with only 31 compute nodes, but readers will recognize thata global combining network (106) optimized for collective operations foruse in RDMA in a parallel computer in accordance with embodiments of thepresent invention may contain only a few compute nodes or may containthousands of compute nodes.

In the example of FIG. 5, each node in the tree is assigned a unitidentifier referred to as a ‘rank’ (250). The rank actually identifies atask or process that is executing a parallel operation according toembodiments of the present invention. Using the rank to identify a nodeassumes that only one such task is executing on each node. To the extentthat more than one participating task executes on a single node, therank identifies the task as such rather than the node. A rank uniquelyidentifies a task's location in the tree network for use in bothpoint-to-point and collective operations in the tree network. The ranksin this example are assigned as integers beginning with 0 assigned tothe root tasks or root node (202), 1 assigned to the first node in thesecond layer of the tree, 2 assigned to the second node in the secondlayer of the tree, 3 assigned to the first node in the third layer ofthe tree, 4 assigned to the second node in the third layer of the tree,and so on. For ease of illustration, only the ranks of the first threelayers of the tree are shown here, but all compute nodes in the treenetwork are assigned a unique rank.

For further explanation, FIG. 6 sets forth a flow chart illustrating anexample method for messaging in a parallel computer (100) using RDMAaccording to embodiments of the present invention. The parallel computer(100) of FIG. 6 includes a plurality of nodes (102 a, 102 b). In theexample of FIG. 6, each node (102 a, 102 b) may be embodied, forexample, as a compute node, an I/O node, or other module of automatedcomputing machinery that forms a parallel computer (100).

In the example of FIG. 6, each node (102 a, 102 b) includes a messagingunit (101 a, 101 b). The messaging units (101 a, 101 b) of FIG. 6 may beembodied, for example, as a communications adapter for point-to-pointdata communications with other nodes in the parallel computer (100), asa library of data communications operations for carrying out datacommunications with other nodes in the parallel computer (100), or anycombination thereof. In the example of FIG. 6, the messaging units (101a, 101 b) may carry out data communications with other nodes in theparallel computer (100), for example, over a torus network as describedabove with reference to FIGS. 1-4.

The example method of FIG. 6 includes receiving (601), by a kernel (103a) of the first node (102 a) through an API (109 a), a send work request(111). The API (109 a) of FIG. 6 may include one or more softwareroutines that an application-level program can invoke to initiate a sendwork request (111). In the example of FIG. 6, a work request representsa request for the recipient of the work request to perform some task.The send work request (111) of FIG. 6 is a particular type of workrequest. The send work request (111) of FIG. 6 represents a request forthe recipient of the send work request (111) to perform the task ofsending data to another node. In the example of FIG. 6, the send workrequest (111) is received (601) by the first node (102 a), and as such,the send work request (111) represents a request for the first node (102a) to perform the task of sending data to another node, designated hereas the second node (102 b).

In the example method of FIG. 6, the send work request (111) includes alocal virtual address (113) on the first node (102 a) from which data isto be transferred. The local virtual address (113) of FIG. 6 points to alocation in virtual memory of the first node (102 a) that is mapped toactual physical memory of the first node (102 a), for example, by a pagetable that is accessible by the kernel (103 a). In the example method ofFIG. 6, the send work request (111) also includes a specification of asize (115) of data that is to be transferred from the first node (102 a)to the second node (102 b).

In the example method of FIG. 6, data can be transferred from the firstnode (102 a) to the second node (102 b) by exchanging messages between amessaging unit (101 a) of the first node (102 a) and a messaging unit(101 b) of the second node (102 b). Such messages may have a predefinedpacket size to include control information such as the address of therecipient, as well as a payload representing the actual data that is tobe transferred. In the example of FIG. 6, the size (115) of data to betransferred from the first node (102 a) to the second node (102 b) islarger than a messaging packet size for sending data from the first node(102 a) to a second node (102 b). Because the size (115) of the data tobe transferred from the first node (102 a) to the second node (102 b) islarger than the messaging packet size, transferring the data referencedin the send work request (111) by exchanging messages between themessaging unit (101 a) of the first node (102 a) and the messaging unit(101 b) of the second node (102 b) would necessitate exchanging multiplemessages.

The example method of FIG. 6 also includes translating (602) the localvirtual address (113) on the first node (102 a) to a physical address onthe first node (102 a). The physical address represents the physicaladdress in memory from which data is to be transferred. In the exampleof FIG. 6, translating (602) the local virtual address (113) on thefirst node (102 a) to a physical address on the first node (102 a) maybe carried out, for example, by looking up the virtual address (113) ina page table stored on the first node (102 a), by looking up the virtualaddress (113) in a TLB stored on the first node (102 a), by using anaddress translation algorithm, and so on.

The example method of FIG. 6 also includes creating (604), by the kernel(103 a) of the first node (102 a), a local RDMA object (107 a) thatincludes a counter set to the size of a messaging acknowledgment field.In the example of FIG. 6, a messaging acknowledgment field represents adata structure used to store acknowledgement data that is sent inresponse to the receipt of a message. For example, if the first node(102 a) sent a message to the second node (102 b) using the messagingunit (101 a) in the first node (102 a), the first node (102 a) wouldexpect to receive acknowledgment data from the second node (102 b)indicating that the message was received by the second node (102 b).Such acknowledgment data may include information used to verify that themessage was received correctly such as, for example, a checksum. In theexample of FIG. 6, the acknowledgment data would be written into amessaging acknowledgment field in computer memory of the first node (102a). Because the local RDMA object (107 a) includes a counter set to thesize of a messaging acknowledgment field, as acknowledgment data isreceived by the first node (102 a), the first node (102 a) may decrementthe counter for the purpose of determining when all acknowledgment datahas been received. In the example of FIG. 6, the size of a messagingacknowledgment field may be expressed in any unit of measure, forexample, such as byte, kilobyte, megabyte, and so on.

The example method of FIG. 6 also includes sending (606) a message froma messaging unit (101 a) in the first node (102 a) to a messaging unit(101 b) in the second node (102 b). In the example of FIG. 6, themessage includes a RDMA read operation request (612), the physicaladdress (614) of the local RDMA object (107 a), and the physical address(616) on the first node (102 a) from which data is to be transferredfrom. In the example of FIG. 6, a RDMA read operation request (612) issent from the first node (102 a) to the second node (102 b), to promptthe second node (102 b) to read data stored in memory of the first node(102 a) into memory on the second node (102 b). In such an example, theRDMA read operation request (612) is accompanied by the physical address(616) on the first node (102 a) from which data is to be transferredfrom, so that the second node (102 b) is informed of the address inmemory on the first node (102 a) that the data is to be read from.

The example method of FIG. 6 also includes receiving (608), by the firstnode (102 a) responsive to the second node's (102 b) execution of theRDMA read operation request (612), acknowledgment data (618) in thelocal RDMA object (107 a). In the example of FIG. 6, acknowledgment data(618) is sent from the recipient of a message to the sender of a messagein response to the receipt of a message. For example, if the first node(102 a) sent a message to the second node (102 b) using the messagingunit (101 a) in the first node (102 a), the first node (102 a) wouldexpect to receive acknowledgment data (618) from the second node (102 b)indicating that the message was received by the second node (102 b).Such acknowledgment data (618) may include information used to verifythat the message was received correctly such as, for example, achecksum. In the example of FIG. 6, the acknowledgment data (618) iswritten into a messaging acknowledgment field in the local RDMA object(107 a) of the first node (102 a).

For further explanation, FIG. 7 sets forth a flow chart illustrating anexample method for messaging in a parallel computer (100) using RDMAaccording to embodiments of the present invention. The example method ofFIG. 7 is similar to the example method of FIG. 6 as it also includes:

-   -   receiving (601), by a kernel (103 a) of the first node (102 a)        through an API (109 a), a send work request (111) that includes        a local virtual address on the first node from which data is to        be transferred and a specification of a size of data to be        transferred from the first node to a second node;    -   translating (602), by the kernel (103 a) of the first node (102        a), the local virtual address on the first node (102 a) from        which data is to be transferred to a physical address on the        first node (102 a) from which data is to be transferred from;    -   creating (604), by the kernel (103 a) of the first node (102 a),        a local RDMA object (107 a) that includes a counter set to the        size of a messaging acknowledgment field;    -   sending (606), from a messaging unit (101 a) in the first node        (102 a) to a messaging unit (101 b) in a second node (102 b), a        message that includes a RDMA read operation request (612), the        physical address of the local RDMA object, and the physical        address on the first node from which data is to be transferred        from; and    -   receiving (608), by the first node (102 a) responsive to the        second node's (102 b) execution of the RDMA read operation        request (612), acknowledgment data (618) in the local RDMA        object (107 a).

The example method of FIG. 7 also includes populating (710), by a kernel(103 b) on the second node (103 a), receive work requests. In theexample of FIG. 7, a work request represents a request for the recipientof the work request to perform some task. The receive work requests ofFIG. 7 are a particular type of work request. The receive work requestsof FIG. 7 represent a request for the recipient of the receive workrequests to perform the task of receiving data from another node. In theexample of FIG. 7, the receive work requests reside on the second node(102 b), and as such, the receive work requests represent a request forthe second node (102 b) to perform the task of receiving data fromanother node, designated here as the first node (102 a). In particular,the receive work requests represent a request for the second node (102b) to perform the task of receiving data that was sent from the firstnode (102 a) to the second node (102 b) in response to the send workrequest (111) carried out by the first node (102 a). As such, thereceive work requests can be populated (710) with information such as,for example, the size of data to be transferred from the first node (102a) to the second node (102 b), an identification of the first node (102a) as the sender of the data to be received by the second node (102 b),and so on, such that executing the populated receive work requestscauses the second node (102 b) to receive data that was sent from thefirst node (102 a) to the second node (102 b) in response to the sendwork request (111) carried out by the first node (102 a).

The example method of FIG. 7 also includes receiving (708), by themessaging unit (101 b) in the second node (102 b), the message. In theexample of FIG. 7, the second node (102 b) can receive the message thatincludes a RDMA read operation request (612), the physical address ofthe local RDMA object, and other necessary information over a datacommunications network such as the torus network as described above withreference to FIG. 1-4.

The example method of FIG. 7 also includes creating (712), by the kernel(103 b) of the second node (102 b), a local RDMA object (714) thatincludes a counter set to the size of the amount of data to betransferred from the first node (102 a) to the second node (102 b). Inthe example of FIG. 7, the size of the amount of data to be transferredfrom the first node (102 a) to the second node (102 b) may be included,for example, in the RDMA read operation request (612). Because the localRDMA object (714) includes a counter set to the size of the amount ofdata to be transferred from the first node (102 a) to the second node(102 b), the second node (102 b) may decrement the counter as data (702)is read from the first node (102 a) for the purpose of determining whenall data (702) has been received. In the example of FIG. 7, the size ofthe amount of data to be transferred from the first node (102 a) to thesecond node (102 b) may be expressed in any unit of measure, forexample, such as byte, kilobyte, megabyte, and so on.

The example method of FIG. 7 also includes transferring (706), by one ormore RDMA operations executing on the messaging unit (101 b) in thesecond node (102 b), the data (702) to be transferred from the firstnode (102 a) to the second node (102 b). In the example of FIG. 7, theone or more RDMA operations executing on the messaging unit (101 b) inthe second node (102 b) may be embodied, for example, as computerprogram instructions executing on computer hardware, such as aprocessor, that transfer data between messaging units in nodes. In theexample of FIG. 7, the RDMA operations executing on the messaging unit(101 b) may include, for example, computer program instructions forretrieving data from memory on the first node (102 a), encapsulating thedata to be transferred, and transmitting the data (702) over a computernetwork. In the example of FIG. 7, the RDMA operations transfer datawithout using the central processing unit(s) of the nodes, such that thedata transfers occur without creating heavy workload requirements forthe central processing unit(s) of the nodes.

The example method of FIG. 7 also includes transferring (704), by one ormore RDMA operations executing on the messaging unit (101 b) in thesecond node (102 b), acknowledgment data (618) from the second node (102b) to the first node (102 a). In the example of FIG. 7, the RDMAoperations executing on the messaging unit (101 b) may include, forexample, computer program instructions for retrieving acknowledgementdata from memory on the second node (102 b), encapsulating theacknowledgment data to be transferred, and transmitting theacknowledgment data (618) over a computer network.

In the example of FIG. 7, the send work request (111) is thereby carriedout through the use of RDMA operations rather than through the use ofmessages that are exchanged between the messaging units (101 a, 101 b).That is, data is transferred from the first node (102 a) to the secondnode (102 b), as is requested in the send work request (111), byexecuting an RDMA read operation on the second node (102 b) so as todirectly read the data from memory in the first node (102 a). Similarly,the transfer of data from the first node (102 a) to the second node (102b) is acknowledged by the second node (102 b) by executing an RDMA writeoperation on the second node (102 a) so as to place acknowledgment data(618) in the computer memory of the first node (102 a).

For further explanation, FIG. 8 sets forth a flow chart illustrating anexample method for messaging in a parallel computer (100) using RDMAaccording to embodiments of the present invention. The example method ofFIG. 8 is similar to the example method of FIG. 6 as it also includes:

-   -   receiving (601), by a kernel (103 a) of the first node (102 a)        through an API (109 a), a send work request (111) that includes        a local virtual address on the first node from which data is to        be transferred and a specification of a size of data to be        transferred from the first node to a second node;    -   translating (602), by the kernel (103 a) of the first node (102        a), the local virtual address on the first node (102 a) from        which data is to be transferred to a physical address on the        first node (102 a) from which data is to be transferred from;    -   creating (604), by the kernel (103 a) of the first node (102 a),        a local RDMA object (107 a) that includes a counter set to the        size of a messaging acknowledgment field;    -   sending (606), from a messaging unit (101 a) in the first node        (102 a) to a messaging unit (101 b) in a second node (102 b), a        message that includes a RDMA read operation request (612), the        physical address of the local RDMA object, and the physical        address on the first node from which data is to be transferred        from; and    -   receiving (608), by the first node (102 a) responsive to the        second node's (102 b) execution of the RDMA read operation        request (612), acknowledgment data (618) in the local RDMA        object (107 a).

The example method of FIG. 8 also includes decrementing (804), by thekernel (103 a) on the first node (102 a), the counter by an amount equalto the size of acknowledgment data received from the second node (102b). In the example of FIG. 8, the counter is set to the size of amessaging acknowledgment field. By decrementing (804) the counter by anamount equal to the size of acknowledgment data received from the secondnode (102 b), the kernel (103 a) can determine when all acknowledgmentdata has been received. That is, when the counter is equal to zero thekernel (103 a) can determine that enough data to populate the entiremessaging acknowledgment field has been received, thereby indicatingthat all of the acknowledgment data has been received from the secondnode (102 b). Such acknowledgment data may subsequently be used todetermine whether the message that included a RDMA read operationrequest (612) was received as expected.

The example method of FIG. 8 also includes notifying (806), by thekernel (103 a) on the first node (102 a), a user-level application (802)that the acknowledgment data has been received by the first node (102 a)when the counter is equal to zero. When the counter is equal to zero thekernel (103 a) can determine that enough data to populate the entiremessaging acknowledgment field has been received, thereby indicatingthat all of the acknowledgment data has been received from the secondnode (102 b). As such, the kernel (103 a) may therefore notify (806) theuser-level application (802) that all acknowledgment data has beenreceived by the first node (102 a), so that the user-level application(802) can analyze the acknowledgment data to verify that the message wasreceived by the second node (102 b), to determine that the messageshould be retransmitted, and so on.

In the example method of FIG. 8, notifying (806) a user-levelapplication (802) that the acknowledgment data has been received by thefirst node (102 a) when the counter is equal to zero includes raising(808) an interrupt in the user-level application (802). In the exampleof FIG. 8, raising (808) an interrupt in the user-level application(802) may be carried out by issuing an interrupt request (IRQ)indicating the need for attention by an interrupt handler. Raising (808)an interrupt in the user-level application (802) can cause a contextswitch to the interrupt handler that can signal, to the user-levelapplication (802), that all acknowledgment data has been received by thefirst node (102 a).

In the example method of FIG. 8, notifying (806) a user-levelapplication (802) that the acknowledgment data has been received by thefirst node (102 a) when the counter is equal to zero can alternativelyinclude being (810) polled by the user-level application (802). In theexample of FIG. 8, the user-level application (802) may include computerprogram instructions that enable the user-level application (802) toactively sample to the status of the send work request (111) andsubsequent DMA read operation request, for example, by periodicallychecking the value of the counter in the local RDMA object (107 a).

The example method of FIG. 8 also includes sending (812) an errormessage indicating that the send work request (111) cannot be serviced.In the example of FIG. 8, the send work request (111) may not beserviced, for example, due to a communications failure between the firstnode (102 a) and the second node (102 b), due to an error reading frommemory in the first node (102 a), due to an error writing to memory inthe second node (102 b), and so on. In response to determining that anerror has occurred, an error message can be sent (812) to the user-levelapplication (802) so that the user-level application (802) can retry thesend work request (111) or simply proceed without executing the R sendwork request (111).

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described above with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

It will be understood from the foregoing description that modificationsand changes may be made in various embodiments of the present inventionwithout departing from its true spirit. The descriptions in thisspecification are for purposes of illustration only and are not to beconstrued in a limiting sense. The scope of the present invention islimited only by the language of the following claims.

What is claimed is:
 1. A method of messaging in a parallel computerusing remote direct memory access (‘RDMA’), the parallel computerincluding a plurality of nodes, each node including a messaging unit,the method comprising: receiving, by a kernel of the first node throughan application programming interface (‘API’), a send work request, thesend work request including: a local virtual address on the first nodefrom which data is to be transferred; and a specification of a size ofdata to be transferred from the first node to a second node, wherein thesize of data to be transferred from the first node to a second node islarger than a messaging packet size for sending data from the first nodeto a second node; responsive to the send work request: translating, bythe kernel of the first node, the local virtual address on the firstnode from which data is to be transferred to a physical address on thefirst node from which data is to be transferred from; creating, by thekernel of the first node, a local RDMA object that includes a counterset to the size of a messaging acknowledgment field; sending, from amessaging unit in the first node to a messaging unit in a second node, amessage that includes a RDMA read operation request, the physicaladdress of the local RDMA object, and the physical address on the firstnode from which data is to be transferred from; and receiving, by thefirst node responsive to the second node's execution of the RDMA readoperation request, acknowledgment data in the local RDMA object.
 2. Themethod of claim 1 further comprising: populating, by a kernel on thesecond node, receive work requests; receiving, by the messaging unit inthe second node, the message; creating, by the kernel of the secondnode, a local RDMA object that includes a counter set to the size of theamount of data to be transferred from the first node to the second node;transferring, by one or more RDMA operations executing on the messagingunit in the second node, the data to be transferred from the first nodeto the second node; and transferring, by one or more RDMA operationsexecuting on the messaging unit in the second node, acknowledgment datafrom the second node to the first node.
 3. The method of claim 1 furthercomprising: decrementing, by the kernel on the first node, the counterby an amount equal to the size of acknowledgment data received from thesecond node; and notifying, by the kernel on the first node, auser-level application that the acknowledgment data has been received bythe first node when the counter is equal to zero.
 4. The method of claim3 wherein notifying a user-level application that the acknowledgmentdata has been received by the first node when the counter is equal tozero includes raising an interrupt in the user-level application.
 5. Themethod of claim 3 wherein notifying a user-level application that theacknowledgment data has been received by the first node when the counteris equal to zero includes being polled by the user-level application. 6.The method of claim 1 further comprising sending an error messageindicating that the send work request cannot be serviced.